This study was designed to investigate the development of the discourse function of Japanese postpositional particles"wa"and"ga":"wa"indicating old information and"ga"showing new information.After given an old information, 72 nursery or kindergarten children were presented by tape recorder four types of sentences:(1)sentences with"wa", (2)sentences lacking but requiring"wa", (3)sentences with"ga", and(4)sentences lacking but requiring"ga", and were urged to repeat in the form of a sentence with particle. Preschool children uttered the adequate particle more frequently in the cases of sentences with particle and sentences requiring"ga"than in the cases of sentences laking particle and sentences requiring"wa", respectively. Most frequent errors were due to the deletion of particle.